In the oil and gas production industry, wellbores drilled into the earth to access hydrocarbons from subsurface formations are typically lined with metal tubulars lowered into the wellbore in an assembly of tubulars connected end to end to form a string. Such wellbore lining is generally referred to as casing, and is typically cemented into place once a desired depth has ben reached. Often, after such installation of a first casing string, the depth of the wellbore is extended by drilling a smaller bore through the bottom of the cemented-in casing. Further casing of smaller diameter than the first can then be run into the second bore through the first section of casing and then cemented in place in a similar process.
When running casing into a previously drilled wellbore, a casing string may encounter obstructions preventing it from reaching the desired depth, such as ledges, collapsed borehole sections, or other discontinuities of the wellbore.
Accordingly, there have been publications proposing to cut or mill away such obstructions during running of a casing string driving a rotatable casing shoe that is carried on the bottom end of the casing string and equipped with cutting edges or abrasive elements.
U.S. Pat. No. 7,849,927 and U.S. Patent Application Publication No. 2010/0032170 disclose such solutions, in which the rotatable shoe and the fluid-operated drive mechanism for same are sacrificial, i.e. intended to be left downhole during cementing of the casing string, and are drillable, soluble or degradable so as not to prevent further drilling of the wellbore past the bottom of the cemented casing.
Applicant has developed an improved rotatable shoe and drive configuration which can be used to reduce the parts and complexity of the fluid-operated drive mechanism and recover components thereof from downhole, thereby potentially lowering the cost of such a sacrificial tool.